Abstract

1983

DNA repair mechanisms serve an essential role in preserving genome stability. Differences in the ability and/or the efficiency of DNA damage repair can contribute to varying cancer susceptibilities due to the accumulation of damage over time. A number of processes affect DNA repair including basal transcription, expression induction or suppression, and timing of induction or suppression events. It has been hypothesized that increased susceptibility to cancer in young children is attributed to differences in DNA repair enzymes. To examine potential age-related gene transcription effects caused by DNA damaging agents, human skin fibroblasts were treated with methyl methanesulfonate (MMS). Fibroblasts were derived from 5-month-old and 10-year-old human donors. Real Time and Quantitative RTPCR (RTAQ-RTPCR) was used to measure both basal and MMS-induced expression levels for a panel of MMS-responsive and DNA repair genes. In preliminary experiments, the basal expression of base excision repair (BER) gene polymerase beta was slightly higher in the cells derived from the 5-month-old donor than it was in the cells from the 10-year-old donor. Expression of MMS-responsive genes HERPUD1, HSPA5, and p21 exhibited a greater than 7-fold and 4.5-fold induction above controls in the cell lines derived from the 5-month-old and 10-year-old donors, respectively, after 4 h exposure to MMS. MMS-induction of these genes was slower in the cells derived from the 10-year-old than those derived from the 5-month-old (maximal induction at 8 h versus 4 h, respectively). In the cells from the 5-month-old, induction exceeded 2 and 1.5 fold for Ape1 and polymerase beta, respectively, after 4 h MMS exposure. However, in cells derived from the 10-year-old, Ape1 and polymerase beta exhibited no apparent induction under the same conditions. Our results indicate a possible age-related difference in the magnitude and/or the kinetics of DNA repair gene expression in skin fibroblasts derived from a 5-month-old and a 10-year-old individual. These differences may affect damage repair efficiency and have important implications for the susceptibility of the cell to accumulate DNA damage as a function of age. [This abstract does not necessarily reflect EPA policy]